I have not been able to check it live due to skill points, but during the final beta weekend it seemed as if Deathly Chill (and possibly Chilling Nova) were not proccing during open world pve, where anyone could also apply chill. It seemed like perhaps because the chill was not MY chill, they were not activating. Again, I have no definitive info on live, but I was wondering if there was or is an issue with the way the traits interact with multiple people chilling.